The present invention relates to a shoe press belt for a papermaking machine.
Papermaking machines for removing moisture from a source material of paper are generally equipped with a wire part, a press part, and a dryer part. These parts are arranged in the order of the wire part, the press part, and the dryer part in a wet paper web transfer direction.
A wet paper web is transferred and moisture thereof is removed while the wet paper web is being successively passed through papermaking devices provided in the wire part, the press part, and the dryer part, and the wet paper web is finally dried in the dryer part. In those parts, the papermaking devices corresponding to a function of dehydrating a wet paper web (wire part), a function of squeezing water (press part), and a function of drying the wet paper web (dryer part) are used.
The press part generally comprises one or more press devices arranged in series in the wet paper web transfer direction. An endless felt is disposed in each press device, or an endless felt formed by connecting an ended felt on a papermaking machine is disposed therein. In addition, each press device has a roll press mechanism made up of a pair of rolls facing each other or a shoe press mechanism in which an endless shoe press belt is interposed between a recessed shoe facing a roll and the roll. The felt, on which the wet paper web is placed, is passed through the roll press mechanism or the shoe press mechanism and pressurized while moving the felt in the wet paper web transfer direction, and thereby moisture of the wet paper web is continuously squeezed from the wet paper web by being absorbed into the felt or by passing moisture through the felt to discharge the moisture to the outside.
In the shoe press belt, a reinforcement material is embedded in resin and the resin constitutes an outer circumferential layer, which is brought into contact with the felt, and an inner circumferential layer, which is in contact with the shoe. In addition, the shoe press belt repeatedly travels between the pressurized roll and the shoe, and therefore the resin of the shoe press belt is required to have mechanical properties such as a wear resistance, a crack resistance, a resistance to fatigue from flexing, and a heat resistance, and some studies regarding the resin of the shoe press belt have been carried out in order to improve those required properties (for example, JP 2012-511611T, JP 2008-111220A, JP 2002-146694A, and WO 2013/013891).
In these documents, investigations have been conducted on a belt in which mechanical properties such as a heat resistance, a crack resistance, a resistance to fatigue from flexing, and a wear resistance are improved by selecting, regarding polyurethane, a specific prepolymer, i.e., isocyanate and polyol, and a specific curing agent.